The present disclosure relates to semiconductor structures, and particularly to a metal-oxide-semiconductor field effect transistor (MOSFET) having a high performance replacement gate electrode configured to provide reduced parasitic capacitance and/or low resistance, and methods of manufacturing the same.
A replacement gate metal-oxide-semiconductor field effect transistor (MOSFET) can accommodate a high dielectric constant (high-k) gate dielectric material that is prone to degradation at high temperature due to decomposition or other structural degradation mechanisms. A replacement gate MOSFET is formed by forming activated source and drain regions and optionally metal semiconductor alloys before deposition of a gate dielectric and a gate electrode. Because the gate dielectric and the gate electrode “replaces” a disposable gate structure by filling a recessed region formed after removal of the disposable gate structure, the gate dielectric material, which is typically a high-k gate dielectric material, follows the contour of the recessed region. Thus, use of a high-k gate dielectric material in a replacement gate scheme results in formation of vertical portions of the high-k gate dielectric material as a sidewall structure laterally surrounding the gate electrode formed therein. The high dielectric constant of material of the sidewall results in a significant parasitic capacitance between the gate electrode and the source and drain regions of a replacement gate MOSFET, adversely impacting the performance of the replacement gate MOSFET.
Further, replacement gate MOSFETs typically employ a work function metal portion in each gate electrode such that the work function metal portion contacts the high-k gate dielectric. The work function metals, however, have a greater resistivity than other conductive materials, such as aluminum, that is deposited on the work function metals and fills a predominant portion of the gate electrode. While a horizontal portion of the work function metal portion contacting a top surface of a high-k gate dielectric is required in order to adjust threshold voltage of the replacement gate MOSFET, vertical portions of the work function metal portion located on sidewalls of a gate electrode and laterally surrounding the other conductive material merely increase the resistance of the gate electrode, which includes a U-shaped work function metal portion and an inner conductor portion containing the other conductive material.